Root hairs are tubular polarized extensions of root epidermal cells and are crucial for plant anchorage, nutrient acquisition, and environmental interactions. The plant hormone jasmonate has been reported to promote root hair growth. However, it remains unclear about the molecular mechanisms underlying the stimulation of root hair development by jasmonate.  

In a study published in The Plant Cell, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) revealed a key signaling module in which JASMONATE ZIM-DOMAIN (JAZ) repressors of the jasmonate pathway directly modulate ROOT HAIR DEFECTIVE 6 (RHD6) and RHD6 LIKE1 (RSL1) transcription factors to integrate jasmonate signaling and the root hair developmental process. 

To investigate the molecular mechanisms underlying how jasmonate promotes root hair development, the researchers first confirmed that exogenous application of methyl jasmonate (MeJA) significantly increased the length of root hairs.  

They also discovered that the endogenous CORONATINE-INSENSITIVE1 (COI1) and JASMONATE ZIM ZIM-DOMAIN (JAZ) -mediated jasmonate signaling pathway is critical for root hair development. The disruption of the COI1 receptor or accumulation of a JAZ repressor (e.g. JAZ4 or JAZ8) decreased root hair length. 

Further investigation showed that several JAZ repressors interactedwithRHD6 and RSL1, two bHLH transcription factors crucial for root hair development. JAZ proteins repressed the transcriptional function of RHD6 and interfered with the interaction between RHD6 and RSL1. 

Phenotypic analysis showed that jasmonate promoted root hair growth in a manner dependent on RHD6and RSL1. It also showed that overexpressing RHD6 largely rescued the root hair-defective phenotypes of coi1-2 and JAZ8-ΔJas-9 plants. 

“Our study provides a mechanistic understanding of how JAZ repressors directly regulate RHD6/RSL1transcription factors to integrate jasmonate signaling and root hair development in Arabidopsis”, said Prof. HU Yanru, principal investigator of the study. 

A Simplified Model for Jasmonate-Stimulated Root Hair Development in Arabidopsis. (Image by HAN Xiao)